The neurointermediate lobe of the toad, Xenopus laevis, synthesizes and secretes ACTH, MSH, and endorphin. The lobe is under inhibitory, neural control (via dopamine) from the hypothalamus. We have identified the prohormone (pro-opiocortin) in this system which gives rise to the peptide products. The predominant form has a molecular weight of 31,000 and is glycosylated. Studies on the significance of the carbohydrate on the prohormone, using an inhibitor of glycosylation, tunicamycin, has revealed the role of the carbohydrate on the glycoprotein ACTH precursor to be as a mechanism for selective post-translational cleavage to the correct peptide products.